1. Field of the Invention
The present invention relates to electro-oxidation catalysts, and particularly to methanol electro-oxidation catalysts including rare earth metal oxides and mesoporous carbon, and a method of making the same.
2. Description of the Related Art
The electro-catalysis of methanol oxidation is among the most significant challenges limiting large-scale commercialization of direct methanol fuel cells. In the anode of the direct methanol fuel cell, methanol is directly supplied as a fuel. During methanol electro-oxidation, methanol is oxidized to produce carbon dioxide, electrons, and protons:Pt+CH3OHsol→Pt−COads+4H++4e−  (1)Pt+H2O→Pt−OHads+H++e−  (2)Pt−COads+Pt−OHads→2Pt+CO2+H++e−  (3)
Among all of the metals, platinum (Pt) is believed to be the most active for the electro-oxidation of methanol in an acid environment. In general, for both the cathode catalyst and the anode catalyst, Pt or an alloy containing Pt as a main constituent element is used. However, Pt is very expensive, and during the methanol electro-oxidation reaction, intermediate carbon monoxide is produced, which is strongly adsorbed on the Pt surface. The adsorption of carbon monoxide as an intermediate material in the reaction on the surface of the Pt catalyst deteriorates its catalytic activity, which negatively affects the performance of the direct methanol fuel cell. Thus, in order to realize the success of direct methanol fuel cell technology, new methanol electro-oxidation catalysts having lower percentages of platinum would be desirable.
A number of binary and ternary catalysts for methanol electro-oxidation are known. Most of these catalysts are based on modification of Pt with some other metal(s). Among the various catalyst formulations, Pt—Ru alloys have shown the best results for the methanol electro-oxidation. Following a bi-functional mechanism, the Ru—OH species act as a source of atomic oxygen, which is required for the electro-oxidation of the adsorbed carbon monoxide to carbon dioxide, thus liberating active sites on the surface of the catalyst material near a Pt atom. The reaction steps are described using a bi-functional mechanism as follows:Ru+H2O→Ru−OHads+H++e−  (4)Pt−COads+Ru−OHads→Pt+Ru+CO2+H++e−  (5)
However, the use of the noble metals, such as Pt and Ru, contributes to the high cost of the methanol electro-oxidation catalysts, which affects the overall cost of the direct methanol fuel cell. Thus, development of active methanol electro-oxidation catalysts with lower amounts of Pt and preferably without using Ru at all is desired.
Thus, a methanol electro-oxidation catalyst and method of making the same solving the aforementioned problems is desired.